Transperineal contrast-enhanced ultrasound: a rapid and reliable tool for differentiating abscesses from inflammatory masses in perianal Crohn’s disease

BACKGROUND AND AIM: Perianal abscesses are serious complications of Crohn's disease (CD) requiring timely and accurate diagnosis. Contrast-enhanced ultrasound (CEUS), which in abdominal intestinal ultrasound (IUS) has shown diagnostic performance comparable to CT/MRI in distinguishing intra-abdominal abscesses from inflammatory masses, has not been systematically evaluated in the transperineal assessment of perianal Crohn's disease. This study aimed to evaluate the diagnostic performance, inter- and intra-observer agreement, and diagnostic confidence of transperineal CEUS versus conventional B-mode TPUS in CD patients with perianal symptoms and suspected septic complications. METHODS: We retrospectively reviewed 52 examinations of 37 adult CD patients presenting with painful perianal symptoms and suspected septic complications. Patients were included if TPUS detected lesions > 10 mm requiring CEUS characterization. Exclusion criteria were CEUS contraindications, simple fistulas, or large (>3 cm) obvious abscesses. All examinations were recorded, and three blinded experts independently assessed anonymized videos in random order. Lesions were classified as abscesses, inflammatory masses, or phlegmons. Agreement for lesion size, fluid content, and final diagnosis was evaluated using intraclass correlation coefficients (ICC) and Fleiss-Cohen's kappa (κ). Diagnostic confidence was assessed using a 5-point Likert scale. RESULTS: On B-mode, 17 abscesses, 32 inflammatory masses, and 3 phlegmons were identified. CEUS reclassified several, yielding 16 abscesses, 31 inflammatory masses, and 5 phlegmons. Of the 17 abscesses diagnosed on B-mode, only 4 were also classified as abscesses on CEUS, while 13 were reclassified; conversely, 11 inflammatory masses were reclassified as abscesses. Intra-observer reliability improved from κ = 0.55 with B-mode to κ = 0.95 with CEUS. Inter-observer agreement for diagnosis was poor with B-mode (κ = 0.31) but excellent with CEUS (κ = 0.83). CONCLUSIONS: Transperineal CEUS significantly improves inter- and intra-observer agreement and diagnostic confidence compared with conventional B-mode TPUS when differentiating perianal abscesses from inflammatory masses/phlegmons in CD and frequently leads to lesion reclassification in clinically ambiguous cases.